best way for testing apis code example

Example 1: have you done api testing

I have worked on API testing in my project and I used
POSTMAN for manually testing and REST ASSURED
java LIBRARY for automation.
I used JDBC and it is a Java-based data access technology
used for Java database connectivity. It provides classes and
interfaces to connect or communicate Java application with
database.
JDBC API is a Java API that can access any kind of data
stored in a Relational Database. It enables Java programs to
execute SQL statements.

Example 2: api testing approach

Write suitable test cases for the APIs and use testing techniques 
like exploratory testing, boundary value analysis, positive and negative 
testing for understanding the functionality.

• Verify the calls with combination of two or more value added parameters.
• Define the scope and basic functionality of the API program.
• Define the accurate input parameters.
• Test case execution and comparison of the results with expected results.
• Determining API behavior under conditions like the connection with files,
etc.

- There are different types of output observed of an API also:

The main consideration is returning correct results under any type of 
conditions. Mainly, the output or results observed of an API are divided 
into three sections as follows:
• Returning the result status values as ‘Pass’ or ‘Fail’.
• Result as data or any specific information.
• An event where the call to any API function will initiate the call to 
another API function